This proposal focuses on the significance of sensory feedback to the execution of skilled movements. The aims are to determine how peripheral information is processed within the sensory cortex to influence the activity of the motor cortex. Several aspects of the network of connections which link subdivisions of the sensory and motor cortices will be studied and their relationships to general patterns of cortical information processing will be assessed. Understanding how sensory integration occurs may indicate how the system responds to changes in the flow of information processing. The behavioral significance of the loss of one segment in the processing sequence and compensation for this loss may help to determine how the human sensori-motor system responds to injury. Sensory input, including feedback from muscle afferents in area 3a, impinges on cells in sensory area 2. This area is thought to be a processing center for signals which are relayed to the motor cortex. The relationships of cells in these areas will be studied. The forelimb regions of areas 2, 3a of the sensory cortex and area 4 of the motor cortex will be identified by recording evoked potentials to stimulation of peripheral nerves. Cells in area 2 will be identified as projection neurons to the motor cortex by the retrograde transport of HRP. Area 3a afferents will be identified by lesion induced degeneration. EM analysis of labeled cells will determine the synaptic connectivity of these neurons. Then, the effects of area 3a input on the excitability of cells in area 2 will be studied. Neurons in the forelimb region of area 2 which project to the motor cortex will be identified by antidromic stimulation of area 4. The effect of inactivation of cortical input from 3a in altering the peripheral response of area 2 cells will be tested by examining RP characteristics of identified cells in area 2 before and after inactivation of area 3a input. Similar techniques will be used to determine the effects of sensory pathways in changing the excitability of target cells in the motor cortex. Another aim is to determine if sensory inputs converge onto output cells of the motor cortex and change their excitability. P.T. cells will be antidromically activated. Synaptic activation of the P.T. cells by afferents from areas 2 and 3a will be detected by changes in the interval between antidromic invasion of the initial segment and the soma. Finally, the possibility that 1 input may compensate for loss of the other will be explored. The pathway from area 3a will be disrupted. Lesion induced degeneration will identify area 2 axons. Changes in terminal distribution after 3a loss will be analyzed with the E.M..